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| 1 | +// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT |
| 2 | +// file at the top-level directory of this distribution. |
| 3 | +// |
| 4 | +// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| 5 | +// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| 6 | +// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| 7 | +// option. This file may not be copied, modified, or distributed |
| 8 | +// except according to those terms. |
| 9 | + |
| 10 | +use crate::rustc::hir::{intravisit::FnKind, Body, ExprKind, FnDecl}; |
| 11 | +use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass}; |
| 12 | +use crate::rustc::{declare_tool_lint, lint_array}; |
| 13 | +use crate::rustc_errors::Applicability; |
| 14 | +use crate::syntax::{ast::NodeId, source_map::Span}; |
| 15 | +use crate::utils::{snippet_opt, span_lint_and_then}; |
| 16 | + |
| 17 | +/// **What it does:** Checks for missing return statements at the end of a block. |
| 18 | +/// |
| 19 | +/// **Why is this bad?** Actually omitting the return keyword is idiomatic Rust code. Programmers |
| 20 | +/// coming from other languages might prefer the expressiveness of `return`. It's possible to miss |
| 21 | +/// the last returning statement because the only difference is a missing `;`. Especially in bigger |
| 22 | +/// code with multiple return paths having a `return` keyword makes it easier to find the |
| 23 | +/// corresponding statements. |
| 24 | +/// |
| 25 | +/// **Known problems:** None. |
| 26 | +/// |
| 27 | +/// **Example:** |
| 28 | +/// ```rust |
| 29 | +/// fn foo(x: usize) { |
| 30 | +/// x |
| 31 | +/// } |
| 32 | +/// ``` |
| 33 | +/// add return |
| 34 | +/// ```rust |
| 35 | +/// fn foo(x: usize) { |
| 36 | +/// return x; |
| 37 | +/// } |
| 38 | +/// ``` |
| 39 | +declare_clippy_lint! { |
| 40 | + pub IMPLICIT_RETURN, |
| 41 | + restriction, |
| 42 | + "use a return statement like `return expr` instead of an expression" |
| 43 | +} |
| 44 | + |
| 45 | +pub struct Pass; |
| 46 | + |
| 47 | +impl Pass { |
| 48 | + fn expr_match(cx: &LateContext<'_, '_>, expr: &rustc::hir::Expr) { |
| 49 | + match &expr.node { |
| 50 | + ExprKind::Block(block, ..) => { |
| 51 | + if let Some(expr) = &block.expr { |
| 52 | + Self::expr_match(cx, expr); |
| 53 | + } |
| 54 | + // only needed in the case of `break` with `;` at the end |
| 55 | + else if let Some(stmt) = block.stmts.last() { |
| 56 | + if let rustc::hir::StmtKind::Semi(expr, ..) = &stmt.node { |
| 57 | + Self::expr_match(cx, expr); |
| 58 | + } |
| 59 | + } |
| 60 | + }, |
| 61 | + // use `return` instead of `break` |
| 62 | + ExprKind::Break(.., break_expr) => { |
| 63 | + if let Some(break_expr) = break_expr { |
| 64 | + span_lint_and_then(cx, IMPLICIT_RETURN, expr.span, "missing return statement", |db| { |
| 65 | + if let Some(snippet) = snippet_opt(cx, break_expr.span) { |
| 66 | + db.span_suggestion_with_applicability( |
| 67 | + expr.span, |
| 68 | + "change `break` to `return` as shown", |
| 69 | + format!("return {}", snippet), |
| 70 | + Applicability::MachineApplicable, |
| 71 | + ); |
| 72 | + } |
| 73 | + }); |
| 74 | + } |
| 75 | + }, |
| 76 | + ExprKind::If(.., if_expr, else_expr) => { |
| 77 | + Self::expr_match(cx, if_expr); |
| 78 | + |
| 79 | + if let Some(else_expr) = else_expr { |
| 80 | + Self::expr_match(cx, else_expr); |
| 81 | + } |
| 82 | + }, |
| 83 | + ExprKind::Match(_, arms, ..) => { |
| 84 | + for arm in arms { |
| 85 | + Self::expr_match(cx, &arm.body); |
| 86 | + } |
| 87 | + }, |
| 88 | + // loops could be using `break` instead of `return` |
| 89 | + ExprKind::Loop(block, ..) => { |
| 90 | + if let Some(expr) = &block.expr { |
| 91 | + Self::expr_match(cx, expr); |
| 92 | + } |
| 93 | + }, |
| 94 | + // skip if it already has a return statement |
| 95 | + ExprKind::Ret(..) => (), |
| 96 | + // everything else is missing `return` |
| 97 | + _ => span_lint_and_then(cx, IMPLICIT_RETURN, expr.span, "missing return statement", |db| { |
| 98 | + if let Some(snippet) = snippet_opt(cx, expr.span) { |
| 99 | + db.span_suggestion_with_applicability( |
| 100 | + expr.span, |
| 101 | + "add `return` as shown", |
| 102 | + format!("return {}", snippet), |
| 103 | + Applicability::MachineApplicable, |
| 104 | + ); |
| 105 | + } |
| 106 | + }), |
| 107 | + } |
| 108 | + } |
| 109 | +} |
| 110 | + |
| 111 | +impl LintPass for Pass { |
| 112 | + fn get_lints(&self) -> LintArray { |
| 113 | + lint_array!(IMPLICIT_RETURN) |
| 114 | + } |
| 115 | +} |
| 116 | + |
| 117 | +impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass { |
| 118 | + fn check_fn( |
| 119 | + &mut self, |
| 120 | + cx: &LateContext<'a, 'tcx>, |
| 121 | + _: FnKind<'tcx>, |
| 122 | + _: &'tcx FnDecl, |
| 123 | + body: &'tcx Body, |
| 124 | + _: Span, |
| 125 | + _: NodeId, |
| 126 | + ) { |
| 127 | + let def_id = cx.tcx.hir.body_owner_def_id(body.id()); |
| 128 | + let mir = cx.tcx.optimized_mir(def_id); |
| 129 | + |
| 130 | + // checking return type through MIR, HIR is not able to determine inferred closure return types |
| 131 | + if !mir.return_ty().is_unit() { |
| 132 | + Self::expr_match(cx, &body.value); |
| 133 | + } |
| 134 | + } |
| 135 | +} |
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